A generic fastener, in the form of a bolt, is already known from DE-C2 2,807,364. This previously known fastener, conceived as a bone screw, consists of a threadless middle section, to which are attached, both in the upper, proximal part and the lower, distal part, threads with differing diameters, and pitches which differ from each other but are nonetheless constant in each part. Therefore prior to inserting the bone screw, it is necessary to drill holes of differing diameters with corresponding threads having different diameters but a constant pitch, in each of the bone fragments that are to be joined together. If a thread with a smaller pitch is employed for the proximal part of the shaft, then in screwing in this previously known bone screw, the effect is to bring the two bone fragments closer together and to correspondingly compress the fracture surfaces.
A disadvantage of this previously known fastener, designed according to the principle of two threads with differing pitch, is that it has a threadless midsection, and that the differing distal and proximal threads both have constant pitches. This allows merely a compression between two loose bone fragments, but does not permit a local intraosseous pressure generation which would be desirable for a whole range of applications.
With the previously known fastener, as well as with the other bone screws, what is lacking is a differentially acting force in the proximal area, so that in the proximal area again and again we encounter a zone of small bone thickness, which results in reduced stability of the implant.